1. Field of the Invention
The present invention relates to a substrate processing apparatus, and more particularly, to a cleaning technique in a reaction chamber of a substrate processing apparatus which is a producing apparatus of a semiconductor device used when the semiconductor device is produced on a substrate such as an Si.
2. Description of the Related Art
In a substrate processing apparatus of this kind, it is known that cleaning gas is supplied and exhausted to and from the reaction chamber to clean the chamber (see Japanese Patent Application Laid-open No. 2002-47571).
A conventional producing apparatus of a semiconductor device will be explained with reference to FIG. 7. FIG. 7 is a sectional view showing a conception of a reaction furnace.
In a self-cleaning operation aimed at removing reaction by-product adhering to an inner wall or the like of a reaction tube 1 by desired film-forming processing, a flow rate of etching gas 4 as cleaning gas is controlled to a constant value, and the etching gas 4 is continuously supplied from a gas introducing tube 2 into the reaction tube 1 from a plurality of holes 8 through a gas nozzle 7.
A desired amount of gas is exhausted from the reaction tube 1 by adjusting an opening of a pressure-adjusting valve 5 connected to the gas exhausting tube 3, thereby maintaining a pressure in the reaction tube 1 at a constant value.
In the conventional apparatus and method, however, there is a problem that nonuniform etching and etching remainder are generated.
It is conceived that this is caused because in the conventional technique, the etching gas is supplied while the etching gas is exhausted and thus, the following events occur:
(a) A “flow” is generated toward the gas exhausting tube 3 from the gas introducing tube 2 because of a shape of the reaction tube 1 or a relation between a supplying position and an exhausting position of the gas, most of etching gas is consumed at an upstream portion of the “flow” and the etching gas is less prone to reach a downstream portion of the “flow”.
(b) A degree of diffusion of gas is greater in a location in the reaction tube 1 (i.e., in the vicinity of the gas exhausting tube) where a pressure is low, but the degree of diffusion of gas is smaller in a location in the reaction tube (i.e., an upper end of the reaction tube 1 and the like) where the pressure is high. Therefore, etching gas is less prone to reach a high pressure location in the reaction tube 1.
That is, the “flow” toward the gas exhausting tube 3 from the gas introducing tube 2 is generated, and the etching gas is less prone to reach a portion which is not located along the “flow”.
More concretely, as shown with arrows in FIG. 7, a strong flow portion 11 along the flow of gas is generated from substantially a center portion to a portion close to the gas exhausting tube 3 in the reaction tube 1, and a weak flow portion 12 which opposes the flow of gas is generated in an upper portion in the reaction tube 1. Therefore, a flow rate of gas and a partial pressure are not constant in the reaction tube 1.
In this specification, the term “flow” means intentional airflow generated from the exhausting operation, and a flow caused by diffusion of gas is excluded.